In many applications for the type of oven described by my U.S. Pat. Nos. 4,546,553 and 4,546,553, it is extremely beneficial to emit primarily infrared radiation and to emit more radiant energy at the lower half of the oven than at the upper half. U.S. Pat. No. 4,546,533 suggested that an ideal intensity of the radiant energy for drying and curing coatings occurs when the majority of the total energy emitted is radiated at wavelengths of about 5 microns or greater, i.e., at wavelengths within the infrared electromagnetic spectrum. Moreover, the need to emit more radiant energy at the lower half of the oven than at the upper half is apparent in applications where the heavier mass of the object to be heated or dried is substantially concentrated on the lower portion of the object. Examples of objects of this nature include an automotive body or a truck body. Along these lines, it has been well known in the industry for years that, in general, the hardest exterior surface to cure on a vehicle body is the rocker panel, which is the panel located just under the doors of the vehicle body.
In most of the prior art apparatuses, including the embodiments which are described in my U.S. Pat. Nos. 4,546,552 and 4,546,553, the oven architecture generally limits the degree of control over the temperature distribution of the radiant emitting walls of the ovens. In some oven embodiments, the products of burner combustion, along with excess air, are delivered at a uniform temperature to a chamber, which is defined by walls including the emitting wall, for the purpose of heating the emitting wall uniformly. In other oven embodiments, the combustion chamber is direct-fired with a burner and the products of burner combustion within the combustion chamber are agitated or made turbulent, as further described in U.S. Pat. No. 4,546,553, so as to achieve a uniform temperature distribution on the emitting wall. It should be noted that when the products of burner combustion contained in the combustion chamber are made turbulent, the forced-convection heat transfer coefficient is much greater than when there is laminar flow within the combustion chamber. Therefore, the heat transferred to the radiant emitting wall is primarily forced-convection heat transfer, and the heat transferred by infrared radiation to the radiant emitting wall is essentially insignificant.
In the parent application with Ser. No. 07/702,109, for APPARATUS AND PROCESS FOR GENERATING RADIANT ENERGY, now U.S. Pat. No. 5,230,161, the temperature distribution along the radiant emitting wall is selectively varied by varying the cross sectional area of the combustion chamber, defined by the emitting surface and another wall, through which flow products of burner combustion. The foregoing method of varying the temperature distribution has proven to be very satisfactory. However, this method requires at least two surfaces to contain the products of combustion throughout their path of travel, which predicament is oftentimes undesirable. Moreover, in the previous oven embodiment, it is difficult to achieve very high temperatures at the lower portion of the oven as compared with the upper portion thereof.
Thus, there is a heretofore unaddressed need in the industry for a radiant wall oven and process for generating infrared radiation having a nonuniform temperature distribution so that the temperature of the lower portion of the radiant wall can be selectively adjusted to be significantly higher than the temperature of the upper portion.